State legislatures are in the process of reacting to a federal law, the Transportation Equity Act of the 21st Century, that requires them to enact legislation providing either for alcohol interlock programs or for vehicle impoundment for repeat drunk-driving offenders. Seven studies demonstrate that interlocks markedly reduce DUI recidivism while on the vehicle but have no carryover effect once the interlock is removed. Evidence from interlock research in Alberta suggests that a program of brief motivational interventions provided to first-time offenders can reduce DUI recidivism after the interlock is removed. All studies so far, however, have involved voluntary installation in return for being allowed to drive the interlock-equipped car. Findings from voluntary interlock program research are not adequate to predict positive outcomes from mandatory interlock use required by the new law. Also, the majority does not volunteer for the interlock but drive anyway with sufficient success to make the expense and annoyance of the interlock unattractive. Fewer than 10% of eligible offenders participate in an interlock program. Consequently, the overall effect of interlocks is not yet an important DUI control measure. Courts have the authority to mandate interlock use as a condition of probation. This can result in the majority of DUI offenders entering interlock programs. This study evaluates a court-mandated program to determine whether the interlock is as effective in reducing recidivism when it is forced on to the vehicles of unmotivated offenders. It also tests whether a brief motivational intervention program and group support tailored to the interlock experience can lower drinking and driving that occurs after the interlock is removed. Research to date has shown that following removal of the interlock, participants have the same recidivism rate as offenders who did not choose to install interlocks and remained fully suspended instead. This research builds on experience gained in a 5-year RO1-funded program in Alberta, Canada.